1. Field of the Invention
The present invention relates to crossed-field devices, and more particularly to a non-concentric support for a cathode of a crossed-field amplifier that permits the cathode to be offset with respect to an anode of the amplifier.
2. Description of Related Art
Crossed-field devices, such as magnetrons and crossed-field amplifiers (CFAs), are commonly used to generate microwave RF energy for assorted applications, including radar. The crossed-field devices commonly have a cylindrically shaped cathode centrally disposed a fixed distance from a plurality of radially extending anode vanes. The space between the cathode surface and tips of the anode vanes provides an interaction region, and a potential is applied between the cathode and the anode forming an electric field in the interaction region. A magnetic field is provided perpendicular to the electric field and is directed to the interaction region by polepieces which adjoin permanent magnets. Electrons are emitted from the cathode surface, and are caused to orbit around the cathode in the interaction region due to the crossed magnetic and electric fields, during which the electrons interact with an RF electromagnetic wave moving on the anode vane structure. The electrons give off energy to the moving RF wave, thus generating a high power microwave output signal.
In order to achieve optimum performance from the crossed-field device, it is often necessary to adjust the position of the cathode with respect to the anode vanes. Variations in manufacturing tolerances, materials, and field characteristics can result in the cathode not being optimally located upon manufacture. A common technique for adjusting the position of the cathode with respect to the anode vanes, is to utilize a deformable pole sleeve as part of a support structure for the cathode. By applying a bending force to the pole sleeve, the sleeve can be deformed to tilt the cathode off-axis into a corrected position.
Despite the improvement in cathode performance resulting from optimal adjustment of the cathode position, this technique has numerous drawbacks. First, deformation of the pole sleeve does not have sufficient repeatability in that it is difficult to apply an accurate amount of bending force to the pole sleeve to obtain a desired position for the cathode. Moreover, repeated adjustments in position can ultimately weaken the pole sleeve, rendering the crossed-field device unusable. A second drawback of the technique is that tilting of the cathode axis produces differential relative displacement of the respective end-hats of the cathode, in which a portion of an upper end-hat is drawn to a position closer in proximity to the anode vane tips than an associated portion of a lower end-hat. By disposing the end-hat and vane tips close together at a single region, arcing could occur between the elements at the region, significantly degrading operation of the crossed-field device.
Thus, there is a critical need to provide a cathode for a crossed-field device that is optimally positioned with respect to an associated anode structure without tilting an axis of the cathode.